Extended surface,double wall tubing from strip stock



March 17, 1970 E. P. HABDAS EXTENDED SURFACE DOUBLE WALL TUBING FROM STRIP STOCK 2 Sheets-Sheet 1 Filed Jan. 2, 1968 FIGZ FIG.4

FIGS

INVENTOR' EDWARD P. HABDAS ATTORNEY S March 17, 1 970 a. P. HABDAS 3,500,902

EXTENDED SURFACE, DOUBLE WALL TUBING FROM STRIP STOCK Filed Jan. 2. 1968 2 Sheets-Sheet z FIG.I4

FIG.|5 v

INVENTOR EDWARD P. HABDAS BY V ATTORNEYS United States Patent 3,500,902 EXTENDED SURFACE, DOUBLE WALL TUBING FROM STRIP STOCK Edward P. Habdas, Dearborn, Mich., assignor, by mesne assignments, to Calumet & Hecla Corporation, Allen Park, Mich., a corporation of Delaware Filed Jan. 2, 1968, Ser. No. 695,098 Int. Cl. FZSf 1/14; B21d 53/02; B21k 29/00 US. Cl. 165184 4 Claims ABSTRACT OF THE DISCLOSURE Finned tubing formed from strip having one edge slotted to provide fins, the strip being rolled into tubular configuration and the strips twisted through 90 degrees and wrapped around and attached to the outer surface of the tubing.

Background of the invention The invention relates to the field of heat exchange tubing in which the outer surface of the tubing is extended as for example by the provision of circular or helically extending fins. Fins have in some instances been separately formed and wrapped around and brazed or otherwise secured to the outer surface of plain tubing. Another practice has been to form circular or helical fins by rolling the fins out of the material of the tubing by opposed fin forming rolls.

In addition, tubing without extended outer surface has been formed by rolling strip material into double wall tubing in which the strip material is brazed to produce in effect, solid tubing.

Summary of the invention In accordance with the present invention strip material having a width equal approximately to three times the circumference of the desired tubing i provided along one edge with a multiplicity of parallel slits extending approxi' mately one-third of the way across the strip. The material between the slits is then rotated through 90 degrees so as to present the width of the finning elements thus formed in a plane perpendicular to the plane of the strip material.

Thereafter, the strip is rolled so as to form a double wall tube which will cause the tube to occupy a location at the inner or connected ends of the fin forming elements. These elements are then wrapped around the tubing to form either a multiplicity of axially spaced circumferential fins, or if preferred, each fin may be given a slight lead so that all of the fins together extend at a helical angle. In the latter case the fins may be somewhat longer than otherwise and may be disposed to provide helical fins having one, two or more starts.

The interconnection between the adjacent surfaces of the tube convolutions may be brazed together by the provision of brazing material and the inner edges of the fins may likewise be brazed to the outer surface. of the double wall tube. If the tubing is copper clad steel for example, the copper coating will supply the brazing material to bond the walls of the double wall tubing together and also to bond the inner edge of the fins to the tubing.

It is accordingly an object of the present invention to provide extended surface tubing having the tube proper formed of strip material wrapped into tubular configuration and having integral fins formed by slots along one each of the strip from which the tubing is formed, the fins being wrapped around the outer surface of the tubing and bondetd thereto.

It is a further object of the present invention to provide a method of making extended surface tubing comprising ice the steps of slitting one edge of an elongated strip to provide fin forming portions, wrapping or rolling the unslitted portion of the strip into tubular configuration, twisting the fin elements through '90 degrees to present an edge surface thereof for attachment to the tubing, wrapping the finning elements around the tubing, and bonding the convolutions of the strip together to form integral tubing and bonding the inner edges of the fins to the outer surface of the tubing.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention.

Brief description of the drawings FIGURE 1 is an elevational view of extended surface tubing constructed in accordance with the present invention.

FIGURE 2 is an end view of the tubing shown in FIG- URE 1.

FIGURE 3 is a fragmentary elevational view of a portion of the strip from which the tubing is made.

FIGURE 4 is an end view of the strip seen in FIG- URE 3.

FIGURE 5 is a fragmentary elevational view of the strip provided with fin forming slits.

FIGURE 6 is an end view of the slitted strip shown in FIGURE 5.

FIGURE 7 is a fragmentary elevational view of the slitted strip of FIGURE 5, with the fin elements twisted through degrees.

FIGURE 8 is an end view of the strip shown in FIG- URE 7.

FIGURE 9 is an end view of tubing formed by rolling the unslitted portion of the strip into a tube, the figure being on a substantially enlarged scale.

FIGURE 10 is a side elevational view of the structure shown in FIGURE 9.

FIGURE 11 is a view similar to FIGURE 9, showing the fin elements wrapped around the tubing and bonded thereto.

FIGURE 12 is a side view of the structure shown in FIGURE 11.

FIGURE 13 is a fragmentary elevational view of tubing in which the fin structure is helical.

FIGURE 14 is a fragmentary view shownig the ends of the fin forming portions inclined.

FIGURE 15 is an end view showing finned tubing constructed from the slitted material of FIGURE 14.

Description of the preferred embodiment The extended surface tubing shown in FIGURE 1 comprises a tube proper indicated at 10 formed of an inner convolution 12 and an outer convolution 14, and generally radially extending fin structure 16.

In order to produce a finned tube of this character from a single strip of stock, a method as sequentially illustrated in FIGURES 3-12 is provided. The starting material is an elongated strip 20 formed of metal such for example as copper clad steel, the strip having a transverse width W equal approximately to three times the desired diameter of the tubing 10. As shown in the figures, the tubing is constituted by three longitudinally extended zones each designated 1rD where D represents the approximate diameter of the finishing tubing.

The first step in the production of the extended surface tubing in accordance with the present invention is to provide longitudinally extending slits 22 which extend approximately one-third of the way across the strip 20. The slits 22 define therebetween fin forming portions 24 and the spacing of adjacent slits determines the height 3f the fins as provided on the finished structure. It will be apparent as the description proceeds that an increase in spacing between the slits not only results in an increase in fin height, but it results also in a corresponding increase in spacing between adjacent fin convolutions.

The next step in the production of finned tubing in accordance with the present invention involves the twisting of each of the fin forming portions or elements 24 through 90 degrees so as to present an edge surface 26 of the fin forming elements parallel to the plane of the strip 20 for engagement therewith, as will subsequently appear.

After the fins have been twisted into the relationship illustrated in FIGURE 8, the strip 20 is rolled or wrapped into a double wall tube indicated at 28, the tube having an inner convolution 30 and an outer convolution 32. If the strip 20 is copper clad steel, the copper cladding constitutes brazing material which will unite the abutting surfaces of the inner and outer convolutions 30 and 32 as well as provide bonding material for the fin forming portions 24, as will subsequently appear.

Finally, the individual fin forming elements 24 are now wrapped around the tube 28 to bring the edge surface 26 thereof into engagement with the outer surface of the outer tube convolution 32, as best seen in FIG- URE 11. It is appreciated that the fin forming portions 24 may offer substantial resistance to bending in the plane illustrated in the figures so that it may require lateral support against buckling. This of course varies in accordance with the height of the fin, the tendency to buckling and the resistance to bending being more pronounced as the height of fin increases.

It is within the contemplation of the present invention to permit some limited buckling of the inner edge of the fin to allow for the difference in circumference between its inner edge 26 and its outer edge '34. Alternatively, the wrapping of the fin into the configuration illustrated in FIGURE 11 may be permitted by some stretching and thinning of the fin material adjacent its outer periphery.

In any case, the assembly as shown in FIGURE 12 may be completed simply by retaining the slitted and wrapped strip in the required configuration and subjecting it to heat so as to melt the copper coating and effecting a brazed bonding of the inner and outer convolutions of the tubing to each other.

While the fins as illustrated in the figures are bent into individual circumferentially extending convolutions, it will be appreciated that each fin may if desired be caused to extend at a helix so as to be adjacent to the start of the next succeeding fin whereby all of the fin forming elements are caused to occupy substantially a single helical path. Alternatively, if each of the fin forming elements is Wrapped around the tubing so as to bring its free end into a position contiguous to the second fin forming element rather than the next adjacent fin forming element, the resulting finned structure will comprise a two-start fin each fin of which is composed of the separate segments produced by the individual fin forming elements.

In FIGURE 13 there is illustrated the arrangement in which the individual fins 40 are disposed in a helical configuration on the tubing 42, the free end of each fin being brought into position contiguous to the connected end of the adjacent fin or a fin adjacent thereto.

In the foregoing it will be observed that the free end of each fin is spaced slightly from the attached end of the fin or of the adjacent fins as the case may be, leaving a triangular shaped gap. If desired, the slitting operation may be accompanied with a cutting operation to provide inclined ends 50 so that when the strip is rolled up into a tube and the individual fins are wrapped around the tube, the end 50 of each fin is closely adjacent to the opposite end of the fin, thus eliminating the presence of the triangular gap as shown in the previous embodiments of the invention.

The drawings and the foregoing specification constitute a description of the improved extended surface, double wall tubing from strip stock, in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. Extended surface tubing comprising an integral elongated strip rolled transversely of its length to form a tube having an edge of the strip extending longitudinally of the tube parallel to its axis, said strip having a slitted edge providing fin elements integral with the strip each attached at one end to said tube, said fin elements being twisted through degrees to present an inner edge surface to the tube and wrapped around the tube with the inner edge surface in tight contact with the outer surface of the tube, longitudinally extending portions of said rolled strip being bonded together to form a sealed tube, the inner edges of said fins being bonded to the outer surface of said tube.

2. Tubing as defined in claim 1 in which said fins each form a single circular convolution around said tube.

3. Tubing as defined in claim 1 in which said fins extend helically and the free end of each fin is substantially contiguous to the connected end of an adjacent fin to provide fin structure defining a continuous helical configuration.

4. Tubing an defined in claim 1 in which said strip has an unslitted width such as to form a double walled tube having inner and outer convolutions, and in which the width of the slitted portion of said strip is such that each fin element forms a single convolution around said tube.

References Cited UNITED STATES PATENTS 1,829,979 11/1931 Bundy 113118 X 3,022,049 2/1962 Abbott -184 3,362,058 1/1968 Morris et al. 29-1S7.3 2,537,797 1/1951 Simpelaar 165184 X 3,288,209 11/1966 Wall et a1 165184 3,397,440 8/1968 Dalin 165--184 X ROBERT A. OLEARY, Primary Examiner T. W. STREULE, Assistant Examiner US. Cl. X.R. 

